The studies proposed here will focus on determining how membrane bound kinases interact to control the activity of the luminal membrane phosphate carrier, a transport system that has major impact on determining the rate of transtubular phosphate movement. Specifically, the studies will investigate the relationship between protein phosphorylation and phosphate transport in microvillus membrane vesicles isolated from renal cortical tissue. Activities of and interactions among the nucleotide-dependent protein kinases (cAMP and cGMP activated) and the calcium-dependent protein kinases (calmodulin, and phospholipid activate) will be assessed by measuring sodium gradient stimulated phosphate uptake and by analyzing and identifying the phosphoproteins that they generate. Special attention will be given to determining if the functional effects of these induced phosphorylations are independent, antagonistic, additive or synergistic and if a subset of the phospho-proteins generated are similar. The data obtained from these studies will provide additional information about how intracellular second messengers interact at a biochemical level to control a cellular function.